The dbm library provides access to NDBM databases under Unix.
NDBM databases maintain key/data associations, where both the key and
the data are arbitrary strings. They support fairly large databases
(several gigabytes) and can retrieve a keyed item in one or two file
system accesses. Refer to the Unix manual pages for more information.

Unix:

Programs that use the dbm library must be linked as follows:

ocamlc other options dbm.cma other files
ocamlopt other options dbm.cmxa other files